Thermodynamics and kinetics of the thin film magnesium–hydrogen system

The absorption and desorption isotherms of Mg thin films are determined by electrochemical techniques at room temperature. Up to now, especially for hydrogen desorption from pure Mg, the temperature range for determining the isotherm has been confined to high temperatures. The enthalpy of hydride formation and hydride decomposition is in agreement with the data reported previously; however, the present data are measured directly at room temperature. The dynamic electrochemical responses during hydrogen extraction reveal that at the beginning of the dehydrogenation reaction the rate is mostly impeded by a nucleation and growth mechanism. The desorption isotherm is simulated with a lattice gas model and excellent agreement between experiment and theory is found. The parameters are used to obtain detailed information about the magnesium–hydrogen system.